This invention relates to developing apparatus in electrophotographic copying machines, and more specifically, to a magnetic brush developing apparatus in electrophotographic copying machines, characterized by a stirring and mixing device, in which both developer stripped from a magnetic roll after development, and newly supplied toner are stirred and mixed.
In electrophotographic copying machines, developer composed of a mixture of a colored fine powder called toner and a body called a carrier is used to turn a latent image of an original formed on a photosensitive body of a photoconductive insulating material into a visual image in a development process. Only the toner in the developer is used to develop the latent image, however, and the carrier is recovered, and hence, the toner is gradually used up as a number of copies are made. Because of this, toner must be added to the developer from a toner supplying device.
Fresh toner supplied from the toner supplying device is electrostatically bonded to the carrier in the developer by frictional contact, and therefore both toner and carrier must be efficiently stirred and mixed.
In the event that the electrostatic charge between the toner and the carrier is insufficient, that is, the effect obtained by stirring toner and carrier is insufficient, they will be attracted to the magnetic roll without being sufficiently stirred. As a result, toner is deposited even in the background areas of the latent image, and the copy obtained is poorly formed and contaminated.
The magnetic brush developing apparatus is often limited in size, however, particularly a magnetic developing apparatus for a small electrophotographic copier. Consequently, the developer is not sufficiently stirred and mixed with the fresh toner, resulting in the problem described above.